In general, a wheel type construction machine can be driven on a paved road, and can perform a work at a construction work site. However, only a steering system suited to the work is applied at the construction work site. In other words, when a steering handle for a wheel type construction machine is manipulated, a driving or traveling direction of the machine is set. On the other hand, when the steering handle is not manipulated, the driving or traveling direction is fixed.
For this reason, accuracy of the work is increased and an impact is not transmitted to the steering handle when the construction machine travels on an irregular road surface so that safety of an operator can be ensured. On the contrary, when the wheel type construction machine travels on a paved road due to the absence of a driving straightness restoring force, various driving operations are required to control the traveling direction during the traveling of the machine, and thus an operator suffers from a fatigue sensation.
A steering system for a wheel type construction machine in accordance with the prior art as shown in FIG. 1 includes:
a hydraulic pump 1 that is connected to an engine (not shown);
a steering motor 2 that is connected to the hydraulic pump 1;
a steering valve 3 that is installed in a flow path between the hydraulic pump 1 and the steering motor 2 and is shifted to control a start, a stop, and a direction change of the steering motor 2;
a steering handle 4 that operates the steering motor 2 and the steering valve 3 in response to an operator's steering manipulation; and
a steering cylinder 6 that steers the machine operation by changing a direction of wheels 5 by means of a hydraulic fluid that is supplied from the hydraulic pump 1 through the manipulation of the steering handle 4.
When the steering handle 4 is rotatably manipulated in a clockwise direction or a counter-clockwise direction, the steering valve 3 is shifted and the hydraulic fluid discharged from the hydraulic pump 1 can be supplied to the steering cylinder 6 via the steering motor 2.
In this case, when a spool of the steering valve 3 is shifted to the left on the drawing sheet (i.e., shifted to a first position 3a), the hydraulic fluid discharged from the hydraulic pump 1 is supplied to one-side chamber 6a of the steering cylinder 6 via the steering valve 3 and the steering motor 2 so that the machine is steered to the right. On the contrary, when the spool of the steering valve 3 is shifted to the right on the drawing sheet (i.e., shifted to a second position 3b), the hydraulic fluid discharged from the hydraulic pump 1 is supplied to the other-side chamber 6b of the steering cylinder 6 via the steering valve 3 and the steering motor 2 so that the machine is steered to the left. That is, the traveling direction of the machine is controlled by changing a direction of the wheels 5 linkably connected to the steering cylinder 2.
In the meantime, when the steering valve 3 is in a neutral mode (i.e., in a neutral position 3c), a flow path between the steering motor 2 and the steering cylinder 6 is blocked in a disconnected fashion. For this reason, since a force from the wheels 5 is not transmitted to the steering motor 2, the steering system entails a problem in that it does not have a driving straightness restoring force.